Isotope modeling with CESM

Transcription

1 Isotope modeling with CESM Alexandra Jahn Depart. of Atmospheric and Oceanic Sciences & Institute for Arctic and Alpine Research University of Colorado at Boulder With contribu,ons from B. O3o- Bliesner and E. Brady (NCAR) and the CESM Isotope Development team: Z. Liu 2, D. Noone 4, K. Lindsay 1, M. Vertenstein 1, D. Bailey 1, F. Joos 3, A. Bozbiyik 3, A. Ge3elman 1, S. Gu 2, C. Koven 5, E. Kluzek 1, J. Nusbaumer 4,7, B. Riley 5, J. Tang 5, P. Thornton 6, X. Wen 2, T. Wong 4, J. Zhang 2, J. Zhu 2 1. National Center for Atmospheric Research, 2. University of Wisconsin, Madison, 3. University of Bern, 4. Oregon State University, 5. Lawrence Berkeley Laboratory, 6. Oak Ridge National Laboratory, 7. University of Colorado, Boulder

2 What are isotopes? Isotopes are variants of an element with additional neutrones à these lead to small differences in the physical properties of the element Radioactive or unstable isotopes break down by radioactive decay at a constant rate to produce a daughter element The half life of a radioactive isotope is the time it takes for 50% of the original nuclei in a sample to decay to the daughter element

3 Fractionation The small differences in the physical proper3es of each isotope affect how isotopes are par3oned between different parts of the climate system à this is called frac3ona3on Due to frac3ona3on, isotopes can be used to measure environmental changes Oxygen and hydrogen Isotopes help us measure temperature and ice volume Carbon isotopes help us infer changes in the ocean circula3on and in the biological produc3vity, as well as use radiocarbon as clock

4 98.89% 1.11% <0.01% Isotope Delta Notation H 2 16 O H 2 18 O Light Oxygen Heavy Oxygen (0.2% of all oxygen, 11% heavier than light oxygen)

5 Many climate proxies are inferences of past climate change from isotopic records in archives like sediment and ice cores Fig. courtesy of N. Rosenbloom, Deep Time Liaison

6 Observed Oxygen isotope distribu;on of precipita;on over land Lowest values of δ 18 O towards the poles, meaning more 16 O reaches these latitudes than 18 O Ice sheets are located at high latitudes, so depleted in 18 O

7 Temperature Effect for δ 18 O in Precipita;on Less depleted δ 18 O in Snow vs. Temp. Paleo-Thermometer Δ(δ 18 O) ~0.7[ o / oo /K] ΔT Spatial relationship Observed to hold temporally over seasons and interannually in ice cores. More depleted Colder Jouzel et al Warmer But can the modern relationship be used to reconstruct high-latitude temperature change over the long time periods of Glacial- Interglacial change?

8 CCSM3 TraCE, Transient Simulation of the Last Deglaciation Forcing: 60 o N June Insolation(Orbital) Atm CO2 concentration (+Ice Sheet orography) Meltwater input NH SH Proxy Comparison δ 18 Op* over Greenland From IsoCAM3 slices Greenland SAT CCSM3-Full CO2+IS, Orbital+IS δ 18 O GISP2 Record *δ 18 Op ~ w/offset for bias Liu Z et al. PNAS 2012;109: CCSM3 suggests weaker YD cooling But, Iso-CAM3 agrees better with Δδ18Op

9 Carbon isotopes as ocean tracers Curry and Oppo (2005 ) The δ 13 C ra3o of shells is a measure of how much photosynthesis is taking place in the oceans and/or how much organic material is removed from the surface to the deep ocean via circula3on, as both processes enrich the water in 13 C à paleo proxies mainly use δ 13 C as a water mass tracer, neglec3ng biological produc3vity changes δ 13 C can be used as tracers of carbon cycle processes à e.g., used to diagnose the oceanic uptake of anthropogenic CO 2 Δ 14 C is used as ocean reservoir age tracer

10 Isotope- enabled CESM for studying abrupt change Bette Otto-Bliesner, Zhengyu Liu 2, and icesm Team*** ***E. Brady, A. Jahn 7, D. Noone 4, K. Lindsay 1, M. Vertenstein 1, D. Bailey 1, F. Joos 3, A. Bozbiyik 3, A. Gettelman 1, S. Gu 2, C. Koven 5, E. Kluzek 1, J. Nusbaumer 4, B. Riley 5, J. Tang 5, P. Thornton 6, X. Wen 2, T. Wong 4, J. Zhang 2, J. Zhu 2 1. National Center for Atmospheric Research, 2. University of Wisconsin, Madison, 3. University of Bern, 4. Oregon State University, 5. Lawrence Berkeley Laboratory, 6. Oak Ridge National Laboratory, 7. University of Colorado, Boulder

11 icesm: Water Isotopic and Carbon isotope tracers development Carbon Isotopes Water Isotopes Atmosphere (icam5) Fortunat Joos, A. Jahn, Chengfei He icam C. Bardeen! D. Noone J. Nusbaumer iclm D. Noone! T. Wong icpl M. Vertenstein E. Kluzek E. Brady J. Zhu ipop! J. Zhang E. Brady J. Zhu Ocean (ipop2) A. Jahn, K. Lindsay Coupler Land (iclm4.5) A. Bozbiyik Fortunat Joos irtm! J. Zhu icice! D. Bailey A. Jahn J. Zhu Sea ice (CICE) TBD River Model (irtm) TBD

12 Coupled icesm water isotopes Legrande and Schmidt, 2006 Legrande and Schmidt, 2006

13 Cross sections of oceanic δ 13 C (1990s) Cruise data compiled by SchmiZner et al. (2014) icesm simula3on Jahn et al. (2015), GMD

14 Cross sections of Radiocarbon Cruise data compiled by SchmiZner et al. (2014) GLODAP (Kay et al. 2004) Bio3c Radiocarbon Simula3on Abio3c Radiocarbon Simula3on Jahn et al. (2015), GMD Too old radiocarbon ages in deep Pacific à shows model biases in that region

15 Paleo Application: itrace simulations itrace will allow us to evaluate the skill of CESM, stability through time of the interpretations of the proxies, and the mechanisms associated with abrupt changes of the last 21,000 years Most of the isotope capabilities will be available to the community in CESM2 (to be released in Dec. 2016) Water isotope itrace: Funded by NSF-P2C2: PIs: B. Otto- Bliesner (NCAR), Z. Liu (U. Wisc.), P. Clark (OSU) Carbon Isotope O-iTraCE: Funded by NSF-P2C2: PIs: A. Jahn (CU) and Z. Liu (U. Wisc.)

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